Ultra-wideband (UWB) communication technology has been known for decades. Actually, in 1887, German physicist Heinrich Hertz, discovered radio waves by using a spark gap transmitter, which can been considered as an early UWB radio. That is, the first radio transmission ever made employed UWB technology. Later the use of UWB radios was banned because they use a relatively wide spectrum and therefore UWB technology was not used in commercial communication applications for a long time. However, in late 1990s, the use of UWB technology was brought up again and in 2002 FCC (Federal Communications Commission) permitted the marketing and operation of UWB devices in the USA, which enables public use of UWB communications. It is likely that public use of UWB communications will be allowed also in other parts of the world.
The FCC regulations permit the usage of UWB transmission for communication purposes in the frequency band of 3.1-10.6 GHz. With current ruling the transmitted spectral density has to be under −41.3 dBm/MHz and the utilized bandwidth has to be higher than 500 MHz.
In general, UWB devices operate by employing very narrow or short duration pulses that result in very large or wideband transmission bandwidths. That is, information is sent over the air by using pulses instead of continuous wave, which is used in most of the conventional radios. The frequency, in which the pulses are repeated (Pulse Repetition Frequency, PRF), can be selected to be lower than the channel coherence time (1/delay spread of the channel) of the respective communication link so that there is no need for equalization in the receiver. Therefore, there is a certain guard time between the pulses. Because the spectrum used for UWB communications is in GHz range, the used pulses have to be very short in order to fulfill the spectrum requirements. Depending on utilized technology, the pulse lengths are typically around a couple of pico- or nanoseconds, while the guard time between the pulses may be in the scale of tens or hundreds of nanoseconds.
So-called Impulse Radio (IR) concept is one of the technologies that fulfill the requirements set to UWB technologies. In IR the data is sent by using short baseband pulses, that is, there is no carrier included in the transmission. Also so called RF gating type of impulse radio can be used in UWB communications. Therein the actual pulse is a gated RF pulse, which is a sine wave masked in time domain with a certain pulse shape.
A basic IR transmitter is relatively simple, since in its simplest form an IR transmitter comprises basically only a pulse generator and an antenna. Because transmission power in an IR radio is low, there is no need for a power amplifier, and because signaling is baseband signaling, there is no need for a mixer or for a VCO (Voltage Controlled Oscillator) An IR receiver is more complex than the IR transmitter. Nevertheless, an IR receiver is simpler than a conventional continuous wave receiver, at least in principle, since in an IR receiver, there is no need for intermediate frequencies or filters, which simplifies the receiver.
UWB communications are typically short range, high speed, peer-to-peer communications, that is, communications between two end-user devices. In present UWB communication applications, a physical communication channel is shared between uplink (data transmitted from a first end-user device to a second end-user device) and downlink (data transmitted from the second end-user device to the first end-user device) in a time division type of manner. That is, the physical communication channel is divided into time slots in time domain and some of the time slots are allocated to the downlink and some of the time slots are allocated to the uplink. Link control information, such as acknowledgement messages, which is needed for maintaining the communication link between the communicating parties, is sent in the same physical channel with the actual data.
Since UWB communications are still in the development phase, all details of commercial UWB applications have not been agreed on yet and many details may still require further considerations.